1. Field of the Invention
This invention is directed to a method and apparatus for laminating dry films onto printed circuit boards, in general, and to a relatively inexpensive method and apparatus for laminating the films to printed circuit boards in an inexpensive manner, in particular.
2. Prior Art
The use of dry films in the preparation of printed circuit boards is well known in the art. The dry film technique has been used for several years and is used instead of other techniques which include the placement of a liquid form of material on a printed circuit board to act as a mask. The wet film or liquid layer technique has many disadvantages which are known in the art. These disadvantages include lack of uniformity, poor registration, filling in between the circuit traces and so forth.
The dry film technique has been used to avoid some of the liquid film techniques. In the dry film technique it is usual that large rolls of a "dry film" are placed adjacent to a machine and fed into the macine automatically or semi-automatically, placed next to the printed circuit board and treated appropriately. However, there are only a small number of these types of machines available. These machines are generally quite large and expensive and are not usually suitable or economically feasible for small circuit board houses or the application of small lots of custom circuit boards. A typical example of a known dry film device is the Dupont dry film solder mask vacuum laminator.
As is well known in the art, these dry film techniques are very expensive and difficult for the average circuit board house to amortize. Thus, in the past, small circuit board houses (i.e. relatively small establishments which make printed circuit-board products in small quantities) which wish to use dry film techniques have encountered substantial labor-intensive activities insofar as the films must be placed on the circuit boards by a hot roll laminator and moved, removed, or the like. Even with diligent care, this part of the operation is frequently performed less than perfectly which results in the dry film being placed on the printed circuit board improperly so that defective circuit boards are produced as a result. For example, applying a dry film solder mask to an etched printed circuit board with a hot roll laminator normally results in poor encapsulation of the circuit traces, poor adhesion, trapped air between the traces, and excessive blistering during the wave soldering and hot solder coating operations. The blistering and flaking of dry film off of the circuit board during the hot solder coating operation contaminates the solder bath so that the circuit board cannot be fabricated in the wave solder apparatus.